Quantum key distribution: Real-time compensation of interferometer phase drift

Quantum key distribution: Real-time compensation of interferometer phase drift

a master thesis done in Quantum Cryptography Project at the Department of Electronics and Telecommunications

Student:	Alexey Brylevski, overclocker@pisem.net — exchange from Radiophysics Department, St. Petersburg State Technical University
Supervisor (Norway):	Professor Dag Roar Hjelme
Supervisor (Russia):	Vladimir Kuptsov, kuptsov@radio.rphf.spbstu.ru
Delivered:	February 2002

The results were subsequently published in a paper.

Download

The thesis is available both in English and in Russian, in two formats:

English version: MS Word 97 (400KB) or PDF (410KB)
Russian version: MS Word 97 (380KB) or PDF (870KB; may be slow in displaying and printing due to embedded Russian fonts). Russian version does not include the short historical overview. It also lacks the estimation of tolerable phase error and calculation of how many photon counts need be collected to achieve desired accuracy of phase compensation. You can look it up in the English version.

Abstract

Quantum key distribution (QKD) systems are described in comparison to other cryptosystems; the basic key-distribution protocol and different hardware implementations of QKD systems reviewed.

An experimental QKD setup using phase-coding scheme was assembled and tested. A technique for compensating phase drift in real time was developed, implemented and tested. Results show that such a technique will work even on single-photon level, i.e. without adding components such as variable attenuator to the system.

Pictures

that really should have been in the thesis, because they illustrate what kind of construction produces the phase drift we battled:

Bob and Alice, thermoisolation removed

Bob and Alice, mostly covered by thermoisolation. We worked with interferometer in this state.

And here is the LabVIEW VI that the phase adjustment algorithm was finally packed into:

Neat, huh? :))

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